1. Field of the Invention
This invention relates to a surface shape measurement device, and more particularly to a device that measures the shape of the surface of plate-shaped articles such as constructional materials or steel plates.
2. Description of the Related Art
An example of a conventional surface shape measurement device is shown in FIG. 18. In FIGS. 18(a), and 18 (b)21a to 21e are a plurality of distance measuring devices. Measurement subject 22 moves in the direction perpendicular to the surface of the page, and the dotted line indicates a reference plane of measurement subject 22. These distance measuring devices 21a to 21e respectively measure the distance to the measurement surfaces 22a to 22e of measurement subject 22, whose surface shape is thereby found. The principle of the distance measurement is selected depending on the measurement conditions. Examples are triangulation, the optical section method, and the range finder method. This will be referred to as the first prior art example.
As one example of the first prior art, the triangulation is described in detail referring to FIG. 18(b). In this Figure, distance measuring devices 21a to 21e are constructed by scanners 31a to 31e and receivers 32a to 32e, respectively. Scanners 31a to 31e and receivers 32a to 32e are arranged perpendicularly to the direction of the movement of measurement subject 22 shown by an arrow X, respectively. Each pair of scanners 31a to 31e and receivers 32a to 32e in distance measuring device 21a to 21e is arranged in parallel to the direction shown by the arrow X and is arranged separately from each other by a length 1. Receivers 32a to 32e detect the time when measurement surfaces 22a to 22e are lighted by scanning beams from scanners 31a to 31e, respectively. Then distances to the measurement surfaces 22a to 22e from the reference plane are determined based on the detected times, respectively, and the surface shape of the measurement subject 22 is thereby found.
In a second prior art example, a laser beam etc. is used to describe a track on the surface of the measurement subject. This track is picked up by a CCD camera, and the surface shape is found from the bending of the track.
In the first prior art example, a plurality of distance measuring devices are needed. Indeed, to determine the surface shape in detail, a large number of distance measuring devices are required, resulting in high cost. In the triangulation described above, space longer than the length l is required in the direction of the movement of measurement subject 22 for arranging distance measuring devices 21a to 21e.
A system can be adopted in which the light source is scanned, but this also requires a plurality of photodetectors, so the problem is not solved. Also, in the second prior art example, the measurement takes time and so is unsuitable where the measurement subject is moving at high speed. Additionally, the light source usually needs a large amount of power.